Buried ridge (buried heterostrucrture) semiconductor devices are known. Such devices are useful in constructing light emitting or detecting devices, diodes and laser diodes such as those described in U.S. Pat. No. 5,213,998, issued May 25, 1993, U.S. Pat. No. 5,248,631, issued Sep. 28, 1933; U.S. Pat. No. 5,274,269, issued Dec. 28, 1993; U.S. Pat. No. 5,291,507, issued Mar. 1, 1994; U.S. Pat. No. 5,319,219, issued Jun. 7, 1994; U.S. Pat. No. 5,395,791, issued Mar. 7, 1995; U.S. Pat. No. 5,396,103, issued Mar. 7, 1995; U.S. Pat. No. 5,404,027, issued Apr. 4, 1995; U.S. Pat. No. 5,363,395, issued Nov. 8, 1994; U.S. Pat. No. 5,515,393, issued May 7, 1996; U.S. Pat. No. 5,420,446, issued May 30, 1995; U.S. Pat. No. 5,423,943, issued Jun. 13, 1995; U.S. Pat. No. 5,538,918, issued Jul. 23, 1996; and U.S. Pat. No. 5,513,199, issued Apr. 30, 1996.
Various techniques have been used in the manufacturing of such devices. One such technique is a dry etch process using Xe ion beam etching to provide the desired surface features. In ion beam etching, a mask layer covers a portion of the semiconductor. The ion beam is used to sputter off the exposed portions of the semiconductor. The portions of the semiconductor that are covered by the mask are not etched. Following the ion etch, the mask is removed, thereby exposing the underlying, unetched material. Overall, ion milling solves anisotropy and resolution limits of wet and dry chemical etch approaches, and can be well controlled with respect to major variables that affect etch performance, such as etch rate and end-point detection. In U.S. Pat. Nos. 5,420,446 and 5,423,943, F. Naria and M. Ozawa teach the use of reactive ion etching (RIE) to achieve selective etching of II-VI layers. In this technique it is found that RIE etches II-VI compounds slower if they contain Mg.
However, ion etching can damage the device. For example, the use of such ion beam etching can lead to accelerated degradation at the edges of the laser ridge. Such damage can lead to reduction in luminescence for laser diode semiconductor devices, as well as increased failure rate of such devices.
Another etching technique uses a chemical etchant which reacts with the deposited layers. Chemical etches typically cause less damage to the device than ion beam etching. However, the art has lacked a chemical etch which is compatible with, and suitable for use in II-VI semiconductor fabrication. Additionally, there is a need for a selective etch process for II-VI semiconductors.